Telephone system



June 2Q? 1933- R G RxcHARDsoN ET AL.

TELEPHONE SYSTEM Filed Nov. 9, 1951 EDC-1n Jah IJ P uziznnu .IJ J1 msj UM. minut., om, NM." l

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Patented June 20, 1933 UNITED STATS PATENT orifice RODNEY G. RICHARDSON', OF' CHICAGO, AND

JQHN I. Bement, or BaOeKrIilLD ILLINoIs, AssrefNoRs, BY iviEsNn ASSIGNMENTS, To associera@ nnaoaitio Lanciare,- TORES, NC Q1? {Eil-CAGO, ll-JLANOLS, llQR-ATIQN QF DELAWARE TELEPHONE SYSTEM Application tiled November 9, 1931.l

The present invention relates to telephone systems in general, being concerned more particularly with automatic telephone systems; and the main object is the production ot a new and improved trunking selector switch for use in an automatic telephone system in which the switches which respond to the controlling impulses to set up the telephone connections have only a simple rotary movement, and are positioned in accordance with the received impulses and re stored to normal position by the saine operating magnet.

The present invention may be considered to be an improvement on the invention disclosed in the application of Vicks et al., Serial No. 519,310, filed March 2, 1931; the improvement consisting generally in the provision of such additional circuit arrangements as are found to be desirable or necessary in actual operation, and in the provision of circuit arrangements for providing for unhainpered flexibility in utilizing all the Contact sets in forming any desired number of contact groups (each Contact group corresponding to a different trunk group) and in apportioning the available contact sets in any desired manner amongst the Various contact groups.

GENERAL DESCRIPTION lt may be pointed out that the system disclosed in the above-inentioned application oi" l/Vicks et al. employs rotary switch mechy anisins which are described as having tittyi' in size amongst themselves. Although by Vtransmission of one end of a group in Serial No. 573,760.

using suitable grading, a trunk group can be formed which is in effect a unitary group but contains many more trunks than there are contact sets allotted to the group in the bank of any one selector, as is well understood; it is desirable, nevertheless, from the standpoint ci securing the greatest possible efliciency in each individual installation, to be able to increase and decrease the num# ber of Contact sets allotted to a Contact group to an extent- `dictated by the relative size and ccsts-pertrunk of the trunk groups concerned. Tothis end, the circuit arrangements have been modified in order to enable the size oi" a Contact group in the bank of a selector to be expanded or contracted at will.l

A feature of the invention is that the wip-` ers of the newly developed selector are advanced over the contacts of a large group in successive stages, the selector receiving as many impulses as may be necessary to allow time for the advance over a large group to take place. Since the selector uses two sets of wipers, each step of the wipers advances them over two trunk lines; and since the selector is designed so that it will take iive steps reliably in the time of the controlling impulse thereto, the time of one impulse is suiiicient to allow the advance of the wipers over a group Vof ten trunks the time of two iinpulses is suflicient to allow the advance of the wipers of the selector over twenty trunks; etc.

A further feature of the present arrangement is that a special terminating conductor is used to mark the end of a group inv the bank of the directing wiper of the selector.

The provision of some additional arrange` a,

ment such as this is made necessary because the arrangement employed `for marking the the hereinbefoie-mentioned application of Wicks et al. cannot be used when a group ,contains more than ten trunks, as will be apparent upon a further perusal of the specification.

According to another feature of the in vention, .contacts of the release and series relays cooperate with each other and with s un off-normal contacts for connecting a source of dial-tone current when the selector is taken for use (used ordinarily only in connection with a first selector) and for substituting a connection to a source of busytone current at the end of the directive movement of the selector; which connection persists if an idle trunk is not found, but is forthwith broken in case an ,idle trunk is found in the selected group.

Another feature of the invention relates to an improved circuit arrangement for preventing the application of busy tone from being interrupted and for preventing the selector from being operated further in case the calling subscriber dials another digit after a busy group has been encountered. This arrangement includes the use of a suitable circuit arrangement for preventing the series relay from reoperating after it has fallen back at the end of a series of impulses to start the trunk-huntingy movement, in which case it cannot reoperate to open the busy tone connection, nor to permit further effective operation of the counting relays which direct the advance of the wipers over the groups of contacts.

Other objects and features of the invention, for the most part incidental to those herein enumerated, willi become apparent upon a further perusal of the specification in connection with the accompanying drawing comprising Figs. 13.

Description of the drawing Referring now to the drawing it shows by means of the usual circuit diagrams a suiiicient amount of the apparatus in a telephone systein embodying the features of the invention to enable the invention to be understood. Fig. 1 is a circuit drawing of the improved selector, and Figs. 2, 3, and 4 are drawings showing alternative groupings of the bank contacts into contact sets.

The selector whose circuits are shown in Fig. 1 has seven wipers, 22-28, there being fifty-one contacts in the path of each wiper, as shown best in Fig. 2. These wipers stand normally on the fifty-first set of contacts, with the cam-controlled, offnormal contacts 41, 42, 43, and 51 normally in the respective open or closed positions indicated on the drawing. The operating magnet 20 is arranged to' be operated in a buzzer-like manner to advance the wipers in a clockwise direction, the wipers being advanced the distance of one contact set each time the magnet is deenergized.

Fig. 2 shows all contacts and all of the seven wipersof the selector and it shows the contact sets divided into seven groups, each group giving accessrto` ten trunks orto a multiple of ten trunks, as is shown in the following table:

Digits Number o! Groups assigned trunks 1 1 10 2 2 30 3 5 1U 4 6 10 5 7 1U G 8 20 7 0 10 As will be seen upon reference to Fig. 3 and to this table, the one hundred contacts of the switch are divided into eight contact groups of varying sizes, and the final group contains a large number' of contact sets, eighteen of which are obtained bycurtailing groups 2 to 4 and 6, so that these groups are no longer in multiples of ten.

As will appear from a further perusal of the specification, if afnumber of contacts which is not divisible by ten is assigned to a group, the contacts which would be required to till up the group to make it an exact multiple of ten are, in effect, added to the final group of contacts.

Fig. 4 shows the Way in which the bank of the directing wiper 25 is wired when the switch of Fig. 1 is used as an inter-office trunking switch in a system employing register translators (ordirectors), wherein the oiiice-designating digits are recorded and translated into an'ofiice code. The contact sets in Fig. 4 are allocated amongst thirteen contact groups in accordance with the following table:

Digits Number of Groups assigned trunks Y 1 1 6 2 2 4 3 f 3 8 4 4 6 f 5 5 22 v 6 8 6 7 9 12 8 11 4 9 12 10 13 6 11 14 4 12 15 6 13 16 10 As will be seen upon observing this table and comparing it with Fig. L1, the contacts have been divided into groups of varying sizes which are net multiples of ten, and the linal group is not a large group as in Fig. 3. This grouping is made possible because the code-digit values in the register-translator may be assigned at will. vt will thus be seen that, by using the register sender to accomplish the desired translation, greater flexibility in the trunk-group sizes er contact-set sizes is attained, and that the number of groups may be increased above ten (being thirteen as illustrated).

DETAILED Dnscmr'rIoN Figs. 1 (md .Q

The invention having been described gen erally, a detailed description of the opera tion of the apparatus shown will now be given. For this purpose it will be assumed that the selector shown in F 1 has its contact bank wired shown in Fig. 2 and that it is seized in the usual course of a telephone call by way of conductors 10, 11, and 12. lt is to be noted that conductor 11 normally extends to battery by way of armature 54 of relay 14, off-normal contacts 51, and resistance ela- This battery connection is to enable the selector to be seized in case the preceding switch is et the battery-searching` type.

Line relay 13 new operates over conducters and 12 and through contacts of relay 18. Upon operating, line relay 13 closes a circuit for release relay 14, whereupon release relay 14 operates and grounds conductor 4148 at its inner-upper armature; replaces the battery potential on conductor 11 with a ground potential at armature 54; prepares an operating circuit tor series relay 15 and counting relays 16 and 17 at its lower armature; prepares test circuits for relays 19 and 18 at armatures 52 and 53; and at its upper armature completes a connection from the dial tone lead l5 to conductor 1G, which connection includes oil-normal spring cl3, condenser 47, and contacts of relays 15 and 18. The ilow of current from the source of dial tone informs the calling subscriber that he may new proceed to dial the iirst digit in the desired number, the selector of Fig. 1 being assumed to be aV iirstselector.

Assuming that the first digit in the desired number is the digitO, ten momentary interruptions are produced in the circuit ot line relay 13 at the calling device on the calling line. Relay 13 is accordingly de energized momentarily ten times. Relay 1st does not tall back during this operation because it is slow acting by virtue of the resistance element shunted arount its winding. Series relayl responds to the lirst impulse in the series of impulses generated at the resting contact at theV armature of reoit relays lay 13. Being slow acting by virtue of the resistance element shunted around winding, relay 15 remains operated throughout the series ot impulses. Upon operating, relay 15 at its lower armature shifts the connection of the directing wiper with operating` magnet 20 so that it includes the "iterrupter contacts 20-a; closes a locking circuit for itseliLn at its inner-lower armature independent of oil-normal contacts 42; exten ds ground potential from the grounded conductor 48 at its inner-upper armature to the contacts associated with the lower armature oit counting relay 16 5 disconnects the dial tone source at its upper armature; and at armatures 49 and 50 opens points in the test circuits ot rela-ys 18 and 19 so as to prevent a premature operation oi2 these relays during the group selecting movement.

1n addition to being delivered to series relay 15, each of the ten impulses is delivered to counting relays 16 and 17, which relays are arranged to direct the group-setting operation ot the selector. As will be explained, relays 16 and 17 both operate incidental to the receipt of each odd-numbered impulse, and they both restore incidental to the receipt of each even-numbered impulse. The arrangement is such that relay 16 operates or restores, as the case may be, at the beginning of the concerned impulse, and relay 17 operates or restores, as the case may be, at the end of an impulse. which relays 16 and 17 operate pointed out:

lvVhen the first impulse or any odd-numbered impulse is delivered through the resting contact of armature 13 and the lower armature oiirelay lei, it passes through the lower armature of relay 17 to the lower winding of relay 16. Relay 16 thereupon operates and closes a circuit at its upper armature for its own lower winding in series with the lower winding of relay 17, to ground through the inner-upper armature 15 and 141. No current flows through this locking circuit, however, as long as the initial circuit is intact. At the same time, the diilerential relay 16 connects up its upper winding in parallel with the upper winding of relay 17 at its lower armature, preparatory to the subsequent restoration of relay 16. Then, when the first iinpulse subsides, relay 16 remains operated in series with relay 17 and relay 17 operates. Upon operating, relay 17 disconnects the impulse conductor from the lower windings et relays 16 and 17 and connects it to the upper windings oi' these relays.

When the second impulse or any evennumbered impulse arrives, a holding circuit is closed for the upper winding of relay 17, and a restoring' circuit for the diierential relay 16 is closed through its upper winding.

will now be its The way in y The current now flowing through the upper Winding of relay 16, through the inner-lower contacts of the relay, neutralizes the magnetic effect of the lower winding, permitting the relay to restore. When relay 16 restores, it opens the locking circuit for the lower windings of relays 16 and 17 at its upper contacts,`while at its inner-lower armature it opens the circuit of its upper windings. Relay 17, however, remains operated through its upper winding until the impulse subsides, whereupon relay 17 restores and again transfers the impulse circuit back to the lower windings of relays 16 and 17 preparatory to reoperating the relays upon the receipt of the next impulse (any odd-numbered impulse). i

The Way in which the wipers 22-28 are advanced across the contact groups will now be explained. Upon reference to Figs. 1 and 2, it will be noted that the wipers 22 to 28 are standing normally on the last set of contacts inthe bank (the fiftysfirst set). It is to be noted, moreover, that conductors 29, 30, and 4S are connected to the contacts in the banks of directing wiper 25 (as seen best in Fig. 2), so as to give a group-bygroup movement to the wipers as the relay 16 is alternately operated and restored. lt will be recalled that relays 15'and 16 both operate at approximately the same time the beginning of the first impulse. lVith relays 15 and 16 both operated, the ground potential on conductor 48 is extended to the odd conductor 29, while even conductor 80 is disconnected, and, therefore, uns grounded. Conductor 29 is connected to the fifty-first contact in the bank of wiper 25, as well as to other contacts in the bant corresponding to different positions of wiper 25, as may be observed. Ground potential is, therefore, extended by way of conductor 29 to directing wiper 25, from whence it extends through the operated lower armature of series relay 15, interrupter contacts 204i, and contacts of relays 19 and 18 to operating magnet 20. Magnet 20 operates in the usualA buzzer-like manner to advance the wipers 22-28, whereupon the wipers .steifY ofiqA t last set of bank contacts, and the other end of the wipers comes into engagement Vwith the first set of bank contacts. The movement does not progress beyond this point iter; the time being because the first contact in the bank of wiper 25 is connected to condiictor 30 (the even conductor), which is not grounded at this time.

When relay 16 restores at the beginning of the second impulse it removes ground potential from the odd7 conductor 2 and places it on the even7 conductor 30, causing the circuit of magnet 20 to be closed anew and the wipers to be driven over the first contact group and into engagement with the rst set of bank contacts in the sec- AContact in the bank of It is to be noted that the final wiper 25 1n group 1 group-terminatingwhicn conductor is ond group.

connected to the ground conductor 41S,

inde l time. The rotating action iper, therefore, continues over this Contact untii wiper engages the unl conductor 29.

'6 is ag in operated to again lound con-h 'ir .1 and ungi'ound con- -uct r f2.9 the wipers are advanced five tons over the first five sets of' bank conid roup, which group comand, therefore, occupies conti requiring fifwipers. Since it is as- `v-/itch cannot be relied upon five steps in the time of circuit cennections are third iipulse (hires the .re contae in in which. the ode conwhile the 'fourth imjch to take five more and treni rs A"oni the Lmidi conconductor BO. ay i6 reoperates rcspoi'isivc mise, conductor 2? again retential in pla :e of conducadvanced the rc- .iecond contact with the third Acsif 'jnating digit i nen, when rel ti; the fifth ponsirc to the sixth i )ai heconn jroundcd and wipcrf-; are ai',

Y p; responsive to the 1, cenductor El() again becomes iper-s are advanced to `4pensive to Vthe ninth iml 2' again becomes i the wipers are :id'=iam:csil over he S [irst t ie l) group. rther impulses are received, .se-

back and at armathe test circuits windings of relays time closing th. busy- 12ulocal operating cirt the in'irinally 'loscii *facts itl-a, and contacts ii cuit ii )suits in the advance of the wipers 22 to 28 over the contacts in grounded 8. The closure of this the selected group (group 0) unless one or the other of the two trunks now engaged by the two wiper sets is idle, in which case one or the other of the relays 18 and 19 operates immediately. and interrupts the circuit of magnet 2O before magnet 2O has had time to operate. lt will be assumed, however, for the purpose of the present description, that neither wiper set is in engagement with an idle trunk, in whichcase the magnet 2O operates in a step-by-step manner to advance the wipers over the contact sets in the selected group.

It is assumed further that the advance continues until the wipers encounter the contacts to which conductors 81 to 88 and 34 to 36 are connected. lVhen this contact set is reached, relays 18and 1.9 both operate in case both trunk lines are idle (an idle trunk line being marked by a battery potential such as the battery potential normally impressed on conductor 11 by way of resistance element. 44). The circuit of magnet 2O is, therefore, interruptedy at two points, preventing the further advance of the wipers. Relay 19 closes a locking circuit for its lower winding at its innerlower armature;v and at its lower armature and at its two upper armatures it disconnects wipers 22, 23, and 24 and substitutes wipers 26, 27, and 28.

Relay 18, upon opening a. point 1n the circuit of operating magnet and its innerlower armature, closes a lockingv circuit for its lower winding in series with magnet 20 (magnet 20 does not operate in series with the lower winding of relay 18 because of the relatively high resistance of the said winding) opens a point in the test circuit of relay' 19 and connects up wiper 27 to the incoming release-trunk conductor 11 at its inner-upper armature; and at' its upper and lower armatures it disconnects conductors 10 and 12 from the windings of the line relay 13 (theppby stopping the application of busy tone to the calling line) and' extends them by way of the operated upper and lower armatures of relay 19 to wipers 26 and 28.

vVhen this occurs, the usual line and release relays in the switch connected to the distant end of conductors 84-86 operate, and tne latter applies ground potential to conductor to hold the selector of Fig. 1 in operated position. This ground potential is supplied, of course, before release relay 14 has had time to fall back responsive to the deenergization of the disconnected line relay 13. 1t is to be noted that a momentary impulse is transmitted to the lower winding of relay 16 through contacts of release relay 14 in the interval required for relay 14 to fall back after its circuit is opened by relay 13. The momentary energization of relay 16V at this time does not cause any harm to result, and relay 16 merely falls back again when relay 14 falls back.

Release of he established connection When the connection established through the selector of Fig. 1 is to be released, ground potential is disconnected from conductor 35 of the trunk seized through wipers 26S- 28, whereupon relays 18 and 19 fall back. All of the relays of the selector of Fig. 1 are now in the normal position as shown in the drawing, but the wipers are in an off-normal position and all of the offnormal contacts are, therefore, in an actuated position. llhe same circuit traced hereinbefore for operating magnet 20 in search of an idle trunk line in the selected group is now re-established through contacts of relays 18 and 19 and interrupter contacts .20-e, normally closed contacts controlled by the lower armature of relay 15, and off-normal contacts 41. As a result, magnet 20 operates in the usual buzzer-like manner to advance the wipers until they arrive upon the fifty-first set of bank contacts, whereupon the off-normal contacts, including off-normal contacts 41, are restored to their normal position, and the wipers stop because the restoring circuit of magnet 20 is opened at normal contacts 41. 1t is to be noted that neither relay 18 nor relay 19 can reoperate to interfere with the restoring operation because the test circuits of these relays are open at armatures 52 and 58 of the now-deenergized release relay 14. It is to be noted further that the idle indicating battery potential is reapplied to conductor 11 by way of off-normal contacts 51 and armature 54 when the switch again arrives in its normal or home posit-ion.

From the description hereinbefore given, it is believed that it will be understood that the trunk'comprising conductors 81-38 is seized by way of wipers 22-24 in case this trunk is idle and the one comprising conductors 34-36 is busy, as in this case relay 19 does not operate to substitute wipers 26-28 for wipers 22-24. Under this condition, relay 19 cannot operate following the operation of relay 18 in case the trunk line accessible by way of wipers 26528 becomes idle immediately, because the test circuit of relay 19 is opened at the inner-upper armature of relay 18. It will be understood further that, in case the trunk line accessible by way of wipers 22-24 is busy while the trunk line accessible by way of wipers 26 to 28 is idle, relay 18 cannot operate until after relay 19 has operated and brought relay 18 under the control of wiper 27, whichl connects with the idle trunk line. In this case relays 19 and 18 operate successively,- while in the previously described example the two relays are operated practically simultaneously.

AZZ-trunks busy 'in the selected group When all trunks in the selected group are busy, the wipers of the selector continue to advance until they arrive upon the last contact set in the group. At this time, a new circuit for operating magnet Q0 is closed by way of directing wiper 25 and the groupterminating-ground conductor 48, which circuit excludes the interrupter contacts QO-a, being closed through the lower, armature of relay 15 and-its resting contact, and contacts of relays 19 and 18. over this circuit and remains operated, thereby preventing a further advance of the wipers of the switch, it being remelnbered that the wipers are advanced upon the falling back of the magnet rather than upon the operation thereof. At contacts 20-5 and QO-c, operating magnet 20 opens the test circuits of relays 18 and 19, preventing these relays from energizing subsequently in case the trunks terminating in the bankcontacts on which the wipers are now standing subsequently become idle.

Since the connection is not extended through to another trunk, and the incoming line remains connected to line relay 13, busytone current over conductor 46 continues to iow back over the calling line by way of off-normal spring 43 and condenser 47, and the calling subscriber is apprised of the busy condition of the trunk group and is expected to replace his receiver and bring about the release of the selector, which take-s place when relay 14 falls back and removes ground from conductor 48. It is to be noted that further dialling on the part of the subscriber does not result in further-directive operation of the wipers because magnet 20 is held operated continuously over the above-traced circuit to wiper 25, regardless of any further agtion on the part of counting relays 16 and 1 It ma be pointed out that the abovedescribed all-trunks-busy condition is not sent back in case one or the other of the trunks connected to the last set of contacts in the group is idle because in this case one or the other of relays 18 and 19 operates to open the circuit of magnet 20 before magnet 20 has had time to operate.

The bank layout of Fig. 3

When the Contact grouping is made as indicated in Fig. 3, the groups are not in multiples of ten, as hereinbefore explained. The operation of the switch of Fig. 1, however, isfnot materially affected by the different grouping, the principal differences being that it does not need to take as many as five steps responsive to certain of the impulses. For example, only two steps are required to advance the switch over the second contact group in Fig. 2, as this group contains Magnet 2O operates` only four trunks (two trunks for each full set of contacts).

It is to be noted that thethird group has nine contact sets therein (eighteen trunks). The contacts in the bank of wiper 25 are connected up-the first five to the even 77 conductor 30, the next three to the odd conductor 29, and the last one to the groupterminating ground conductor 48. The switch wipers, therefore, take five steps responsive to the fourth impulse and four more responsive to the fifth impulse; three of the last four being responsive to ground potential encountered by way of conductor 29, and the fourth being responsive to ground potential encountered over conductor 48.

The bank arrangement of Fz'g.V 4

VrI'he bank layout of Fig. 4 illustrates one grouping that may be used when the selector ofFig. 1 is used in a system employing register senders which translate digits of the office designation into a desired combination of office code digits. When the selector of Fig. 1 is used as an office selector' in a system employing register senders, the contact sets of the selector may be divided into as many groups as desired with any desired apportionment of contact sets amongst the established groups, as the number of impulses in a series is not limited to ten as itv is limited, in practice, in a system not using register senders. It is believed that the arrangement in Fig. y4 will be understood in view of the operation of the selector hereinbefore given and the discussion of Fig. 4 in the general description.

It will be understood, of course, that the arrangement herein disclosed of assigning the digits to the several trunk groups with due regard to the number of steps required to pass over the respective trunk groups, in accordance with their sizes, will be applicable to other rotary type selectors, including those using so-called markers, or ma rking switches, in place of the counting relays as herein disclosed, to direct the selector to the desired group.

What is claimed is:

1. In combination, an automatic switch having groups of lines terminating in the bank thereof, said switch being arranged to respond to a series of impulses and beingl of a fast-operating type so that it will move over a group of lines having not greater than a predetermined maximum number of lines therein in the time allotted 'to one impulse, means responsive to each impulse of a series for driving said switch into association with the neXt succeeding group of lilies in case the group over which it is being driven is not larger than the predetermined maximum size, and means effective when the group of lines over which the switch must ing tWo

Wipers, g a test c1 st W1 1cuit 90 per, means per sets over u time with and mean f the Selector ired group perating 1t ies cietion With the effective When 'the g the o ated to set y condition 1n the selecg the deenerhunting selector 35 k divided into g two ksets of per, aid test 111 ed te both s eifective when group of con- 95 c Contact set 111 er for opening the est relays to pret set in the suc- S relay, and a 1orn1al contacts -tone lead7 y-tonc curcontacts of said ontzicts or Said switchans for operai'J en idle contact set t responsive to Said h s ly, 11nd cach hav position, i1v line i11- a busy ying bus y-tone lead controlled arch of :1n idle cone relay 111 Suid switch controlled g lin sind opel ion of said magnet to for holdin uously oper reventin havin set 111clud1ng a test W1 11 Serie iii-1 l to he closed when the selector 1s o dditionally o movement over the conby an impulse ser normal contacts, conelw the Wipers o to as tin for p 1d megne controlled by further 1m- Contact han und socia hotn of sand w1 d, s driven over a mthout Vfinding :1n 1d .r test Wip said t' a conta for app Suid bus by Saul ofi?- said Series r relu c remy.

gnet and me nd for a 11111151 group 1n 111 t con 1 Te bus .1 eing eutmnatic 1t the saine i of oithe 'ts normal and the 11S relay,

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muis or and co1' ettui p' the 6.111 an automa energizi g all o wipers arranged to be driven over said contact sets successively, an operating magnet, means for operating said magnet intermittently to drive said wipers over said contacts until a desired group oit contacts has been reached, additional means for operating said magnet intermittently to drive said wipers over the contacts in the selected group to bring the wipers into association with an idle contact set, and means ti'liective in case the wipers are driven to the last set of contacts in a selected group and the last Contact set is busy for energizing said op-Y erating magnet and for maintaining it energized continuously in order to prevent the advance of the wipers beyond the last contact set in the group.

11. In combination, a selector switch having access to a group of lines, a driving circuit and means for closing it to cause said selector to be driven over said lines in search of an idle one, means tor opening saiddriving circuit when an idle line is found, said selector having a home position, and means for restoring said opening means to reclose said driving circuit to cause said selector to be driven to its homel position.

12. In an automatic-hunting group-selector having two sets of wipers positioned so that both sets hunt over a group at the same time, a test wiper and an associated test relay or each wiper set, a test circuit for each test relay including the associated test wiper, a test wiper common to both wiper sets, and means controlled by said common wiper and responsive to the end of a selected contact group being reached for separately opening each test circuit.

13. In combination, an automatic switch having its contact bank divided into separately designated groups of varying sizes, said switch being responsive to an impulse series containing a random number of impulses to advance by limiting movement into association with the corresponding group of bank contact-s, there being a designation assigned to a specific large group corresponding to a given number ot' impulses, and a designation assigned to the next succeeding group corresponding to a number of impulses greater by more than one than said given number, while the designation assigned to any group next succeeding a small group not greater than a predetermined size corresponds to an impulse series containing only one more impulse than the series corresponding to the designation ot the said small group. Y

14. In combination, an automatic switch having its contact bank divided into separately designed groups of varying sizes, said switch being` responsive to an impulse series containing'a random number of impulses to advance by a hunting movement into association with the corresponding group of bank contacts, there being a designation assigned to each group immediately following group of not more than a given maximum size, over which the switch can advance in the time ot' one impulse, corresponding to only one impulse more than the number of impulses corresponding to the designation of the group which the said following group immediately follows, and a designation assigned to a group immediately following a group larger than the switch can advance over in the time of one impulse which designation corresponds to a number of impulses greater by more than one than the number ot impulses corresponding to the designation of the said larger group.

15. In combination, an automatic switch having its contact bank divided into separately designated groups of varying sizes, said switch being responsive to an impulse series containing a random number of impulses to advance by a hunting movement into association with the corresponding group of bank contacts, and group-huntingcontrol means in said switch for operating the switch into association with any desired group responsive to a number of impulses varying directly with the number of preceding groups and with the respective sizes of such groups.

16. In combination, an automatic switch having its contact bank divided into successive groups, means responsive to impulses corresponding to group designations for causing said switch to advance in a group hunting operation until it comes into association with the designated group, and for subsequently causing it to advance in a contacthunting operation until it comes upon an idle contact set in the group, certain of said groups being single-unit groups composed oit not more contact sets than the switch can pass in a single limiting movement responsive to a single directing impulse, while other ot said groups are multi-unit groups composed of two or more units of contact sets, each requiring a separate impulse to enable the switch to pass over the entire group in its group hunting operation, and means effective during the contact-hunting operation of the switch tor stopping the Contact hunting operation or not at the end of a unit number of contact sets, depending upon whether the contact group ends with such unit number of contacts or extends beyond.

In witness whereof, I hereunto subscribe my name this 5th day of November, 1931.

RODNEY Gr. RICHARDSON.

In wit-ness whereof, I hereunto subscribe my name this 5th day of November, 1931.

JOHN I. BELLAMY. 

